Bending longeron

John ..........

It has been close to fifty years since I spent my days in the pipe shop at
Todd's Seattle, but memory serves well on this subject. It will be next to
impossible to make those bends without a bender having and internal stretch
die, or "bullet". Tubing with that thin of a wall and making that radius
guarantees wrinkles. Packing it with sand will help, of course.

There are low-temperature alloys with which you can fill the tube and then
bend it cold. You heat the alloy, pour it in the tube, and then melt it out
later. This is a clumsy operation and you may still wrinkle the tube. I
would take it to a pro with the right machine.

If you pack it with sand, put a wooden cork in one end of a long tube - the
longer the better. Stand it vertical, fill with fine, dry sand and then
spend an hour or so beating on the tube with a wooden hammer to pack the
sand. Start at the bottom and work your way to the top, refilling as
necessary. When you reach the top, smash in another plug, further
compressing the sand. We had a 20' hole in the floor of the shop with a
hoist overhead. There were three "rivet" hammers mounted to tap the pipe. We
would very slowly lower the pipe past the rivet hammers. After an afternoon
of constant rivet hammers, take a handful of aspirin.

If you end up with wrinkles, they may be artfully removed with a torch and
hammer, but it is difficult to do and requires much practice.

Regards,
Rich S.

"J.Kahn" wrote in message
.. .
I need to make bends of about 30 degrees in a 3/4 x .049 longeron tube,
with a tight bend radius, no more than 3 inches. Can I do the bend hot
without wrinkling the tube by free bending or do I need a supporting die of
some kind? Anybody have any specific techniques?

John